Computing devices, such as notebook computers, personal data assistants (PDAs), mobile communication devices, and portable entertainment devices (such as handheld video game devices, multimedia players, and the like) have user interface devices, which are also known as human interface devices (HID), that facilitate interaction between the user and the computing device. One type of user-interface device that has become more common is a touch-sensor pad (also known as a “touchpad”). A touchpad replicates mouse X/Y movement by using two defined axes, which contain a collection of sensor elements that detect the position of a conductive object such as a finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touchpad, or by tapping commands on the touchpad itself. The touchpad provides a user-interface device for performing such functions as positioning a pointer and selecting an item on a display. These touch pads may include multi-dimensional sensor arrays for detecting movement in multiple axes. The sensor array may include a one-dimensional sensor array to detect movement in one axis. The sensor array may also be two dimensional to detect movement in two axes.
One type of touchpad operates by way of capacitance sensing utilizing capacitive sensors. The capacitance detected by a capacitive sensor may change as a function of the proximity of a conductive object to the sensor. The capacitance may also change due the surface area of the conductive object that is in contact with the sensing device. The conductive object can be, for example, a stylus or a user's finger. In a touch-sensor device, a change in capacitance detected by each sensor in the X and Y dimensions of the sensor array due to the proximity or movement of a conductive object can be measured by a variety of methods. Regardless of the method, usually an electrical signal representative of the capacitance detected by each capacitive sensor is processed by a processing device, which in turn develops electrical signals representative of the position of the conductive object in relation to the touch-sensor pad in the X and Y dimensions. A touch-sensor strip, slider, or button operates on the same capacitance-sensing principle.
Conventional capacitive touch pads are constructed on four-layer printed and two-layer printed circuit boards (PCBs). For example, U.S. Pat. Nos. 5,869,790 and 6,188,391 describe a four-layer and two-layer PCB, respectively. In a conventional four-layer touchpad, the first and second layers contain the horizontal and vertical sensor elements (also referred to as pads) and interconnecting sensor traces that form the capacitive sensor matrix; the third layer contains a ground plane; and, the fourth layer contains the controller and associated circuitry and interconnections to the capacitive sensor matrix. In some conventional two-layer touch pads, one layer contains the horizontal sensor elements and their corresponding interconnecting sensor traces; the second layer contains the vertical sensor elements and their interconnecting sensor traces; and, the controller resides on either of the two layers. It should be noted that in the field of capacitive touch pads, in reference to multiple-layer touch pads (e.g., “two-layer” or “four-layer” touch pads), the term “layer” is conventionally used to refer to a side of a non-conductive substrate upon which conductive material is disposed. It appears that the conventional meaning of the term “layer” is followed in U.S. Pat. Nos. 5,869,790 and 6,188,391, as discussed in further detail below.
FIG. 1A illustrates a four-layer touchpad as described in U.S. Pat. No. 5,869,790. The first layer 2 resides on the topside of the PCB having sensor traces 4 disposed in the vertical direction. These vertical sensor traces connect to vertically-aligned sensor elements disposed on the first layer (not shown). The second layer 12 resides on the underside of the PCB having sensor traces 13 disposed in the horizontal direction. These horizontal sensor traces connect to horizontally-aligned sensor elements disposed on the second layer (not shown). The third layer 3 is buried in the substrate of the PCB and houses the ground plane, which may connect to the topside or underside of the PCB using conductive traces and vias. Lastly, the fourth layer 14 includes the sensing circuit 15.
FIG. 1B illustrates one conventional two-layer touchpad described in U.S. Pat. No. 6,188,391. FIG. 1B of the present application is a reproduction of FIG. 2 of U.S. Pat. No. 6,188,391 with the addition of reference numbers for some components that were unlabeled in FIG. 1B of U.S. Pat. No. 6,188,391. The conventional two-layer touchpad illustrated in FIG. 1B of the present application contains the following: a capacitive sensor matrix 42, or array, having horizontal sensor elements 45 and vertical sensor elements 43 (represented by diamonds) and interconnecting horizontal sensor traces 44 and vertical sensor traces 46; and, a controller chip 48 disposed on the same side of the PCB 47 as the sensor array 42. Although the horizontal sensor traces 44 and vertical sensor traces 46 appear to reside on the same layer in FIG. 1B, such is only for conceptual purposes to understand the functional inter-relationship of the horizontal and vertical sensor elements of the array 42. As described in regards to FIGS. 1 and 2 of U.S. Pat. No. 6,188,391, which would be apparent to one of ordinary skill in the art, the horizontal sensor elements 43 and their interconnecting row sensor traces 44 reside on a different layer than the vertical sensor elements 45 and their interconnecting column sensor traces 46. The controller chip 48 resides on one of these two different layers. Accordingly, the touchpad illustrated in FIG. 1B is a “two-layer” touchpad.
U.S. Pat. No. 6,188,391 describes the use of screen-printing carbon ink patterning to fabricate some of the conductive sensor traces to realize a two-layer board with the controller chip disposed on the opposite side (i.e., the second layer) of the board as the sensor elements and interconnecting conductive sensor traces (i.e., metal and conductive ink). FIG. 1C is a cross-sectional view illustrating the two-layer touch pad of the purported invention of U.S. Pat. No. 6,188,391. FIG. 1C of the present invention is a reproduction of FIG. 8B of U.S. Pat. No. 6,188,391 with the addition of the controller chip 110. It should be noted that in U.S. Pat. No. 6,188,391 the first layer (referred to as a single composite layer) contains both the horizontal sensor traces 69 and vertical sensor traces 104, as illustrated in FIG. 1C. The second layer is on the underside of the printed circuit board and contains the controller chip 110 (which is not shown in the illustration of FIG. 8B of U.S. Pat. No. 6,188,391 but included in FIG. 1C of the present application for ease of understanding). Accordingly, the touchpad produced using screen-printing carbon ink patterning described in U.S. Pat. No. 6,188,391 is a two-“layer” touchpad because the conductive material that constitutes the controller and associated interconnection circuitry to the array is located on a different side (i.e., layer) of the non-conductive PCB substrate (e.g., constructed from FR4 (Flame Resistant 4) PC board laminate) than that of the conductive material used to form the sensor array.
As can be seen from an inspection of FIG. 1C of the present application (and also FIG. 8B of U.S. Pat. No. 6,188,391), the topside layer containing both the horizontal and vertical sensor element layers is a “composite layer,” as it is referred to by U.S. Pat. No. 6,188,391. In such a composite layer, the vertical, carbon ink, interconnecting sensor traces 104 and the horizontal metal interconnecting sensor traces 69 reside in two different planes. The sensor elements 68 (sense pads illustrated by diamonds) and the horizontal metal interconnecting sensor traces 69 reside in a lower plane 130 than the vertical carbon ink sensor traces 104. The vertical carbon ink interconnecting sensor traces 104 reside on a substantially different plane 140 that is on top of the plane containing the sensor elements and the horizontal metal interconnecting sensor traces 130. Although some portion of the carbon ink sensor traces 104 may dip into the lower plane 130 in areas between the horizontal metal interconnecting sensor traces of the lower plane 130 (otherwise occupied by insulation 103), the carbon ink sensor traces 104 cannot reside in the same area of the lower plane 130 than is occupied by the horizontal metal interconnecting sensor traces 69 and their corresponding horizontal sense pads 68.
The substrate(s) of each of these conventional PCBs are made are constructed of material, such as FR4 composite, that is relatively more expensive than conductive ink on polymer construction of a typical keyboard key matrix. FR1 and FR2 composites may also be used. FR1 and FR2 are lower cost PCB substrates than FR4, but still more expensive than the film construction.
FIG. 1D illustrates a simplified version of a conventional keyboard matrix. A conventional keyboard matrix is constructed as two substrates (e.g., two thin sheets of plastic or polymer, for example, Polyethylene terephthalate (PET), also known as PETE, PETP, or PET-P) with conductive traces (typically silver ink) printed on them, arranged such that when pressure is applied at certain locations, one trace on one sheet makes an electrical connection with one trace at the corresponding location on the other sheet. The keyboard buttons are each positioned over one of these locations, so that when the keyboard button is pressed, pressure is applied to the upper sheet at one of these locations causing it to touch a trace on the lower sheet, causing an electrical contact to be made. Typically, the two sheets are separated by a third sheet with no traces printed, and holes located at each of the button positions, so that when no pressure is applied to the area above the hole, the conductive traces on each of the other two sheets are not in contact. It should be noted, however, that FIG. 1D illustrates a small number of rows and columns, and that conventional keyboard matrices may include more rows and/or columns.
The traces on the two printed sheets are arranged such that each trace on the upper sheet crosses each trace on the lower sheet over a hole once and only once. In this way, each button on the keyboard makes a unique contact between one of the traces on the upper sheet and one of the traces on the lower sheet. Typically, one sheet has eight traces (referred to as the key matrix Rows) and the other sheet has between sixteen and twenty-four traces (referred to as Columns). In this way, an 8×16 or 8×24 matrix is formed, with each key or button corresponding to a single point in the matrix.
The keyboard matrix is connected to a main PCB with the keyboard controller (e.g., keyboard controller integrated circuit (IC)) using a compression contact. These compression contacts may be an inexpensive compression contact.
FIG. 1E illustrates a cross-sectional view of a conventional keyboard matrix coupled to the main keyboard PCB with the keyboard controller. The row traces on the lower side of the upper sheet contact with short traces on the upper side of the lower sheet, and these short connecting traces, and also the column traces on the lower sheet contact to carbon-printed pads on the controller PCB. Typically, a non-conducting rubber elastomer is situated in a groove in the keyboard enclosure, and the matrix sheets are laid over the elastomer (with the contacts on the lower sheet facing upwards). The PCB is placed over the contacts so that the carbon-printed contacts are facing down, making contact with the lower sheet contacts, and the PCB is screwed down with screws into the keyboard enclosure. By screwing down the PCB to the keyboard enclosure, the elastomer is under compression, making a pressure contact between the sheet contacts and the PCB contacts.
FIG. 1F illustrates a cross-sectional view of a conventional keyboard matrix coupled to the main keyboard PCB with the keyboard controller using anisotropic conductive adhesive. Contact between the PCB contacts of the main PCB and the sheet contacts are made disposing an anisotropic conductive adhesive between the PCB contacts and the sheet contacts. Anisotropic conductive adhesives only conduct in one direction, and effectively, behave like a connector in one direction (e.g., up/down), but not in the other directions (e.g., side/side and in/out). Anisotropic conductive adhesives are known by those of ordinary skill in the art, and accordingly, additional details regarding them have not been disclosed.
The construction of these conventional keyboard matrices are very inexpensive compared to the conventional circuit boards used for touchpads. For example, the cost of all 3 sheets together is typically around $0.40, with the area of each sheet being around 100 square inches. This compares with around $0.04 to $0.06 per square inch for a two-layer FR4 PCB and around $0.08 to $0.10 for a four-layer FR4 PCB. Accordingly, for a typical PC keyboard, with a 100 square inch matrix area, the total cost of a FR4 PCB is around $4.00 to $6.00 for a two-layer FR4 PCB and $8.00 to $10.00 for a four-layer FR4 PCB.
In addition, the construction of conventional touchpads is typically thicker than the thickness of the construction of keyboard matrices. This is due to the thickness of the conventional substrate(s) used for touchpads, such as FR4. Typical thicknesses of FR4 PCBs are 1.6 mm and 0.8 mm. FR4 PCBs have a thickness of 0.4 mm is somewhat more expensive, but becoming more widely used, especially in touchpad applications.
In another conventional design, a conventional touchpad can be implemented with a conventional keyboard matrix. Typically, both the conventional touchpad and conventional keyboard matrix each include separately circuit boards connected by an interconnecting wire.
FIG. 1G illustrates a conventional keyboard having a keyboard circuit board coupled to the keyboard matrix substrate. The conventional keyboard has a keyboard matrix substrate to which keyboard matrix traces are disposed to detect when a key of the keyboard has been pressed. The conventional keyboard also has a keyboard circuit board. A keyboard controller (e.g., keyboard controller IC) can be coupled to the substrate of the keyboard circuit board. The keyboard circuit board is coupled to a host via a cable.
FIG. 1H illustrates a system having a conventional keyboard coupled to a conventional touchpad. The conventional keyboard, as described above with respect to FIG. 1G, is coupled to a touchpad circuit board via an interconnecting cable. The touchpad circuit board is a separate circuit board from the circuit board of the keyboard circuit board. A touchpad controller (e.g., touchpad controller IC) can be coupled to the substrate of the touchpad circuit board, as described above, for example, on a back side of the substrate of a 2-layer touchpad.